Sandwich composite elements

ABSTRACT

A device for the application of foaming reaction mixtures to a substrate which makes it possible to apply that foaming reaction mixture uniformly, a process for the production of foaming reaction mixtures using this device, apparatus for producing composites which include the device of the present invention and composites produced using such apparatus are disclosed. Use of the device of the present invention to produce foams makes it possible to produce foams having improved surface quality at higher production rates than were previously possible. The device of the present invention is particularly useful for the production of sandwich composite elements.

The invention relates to a device for the optionally simultaneous andoptionally uniform application of foaming reaction mixtures to asubstrate, to a process for the production of foaming reaction mixtures,to a device for the production of sandwich composite elements, and to aprocess for the production of foamed sandwich composite elements.

There has long been a need for devices for the continuous production ofsandwich composite elements at high production rates. Oscillating mixingheads have hitherto been known from the prior art for the continuousproduction of sandwich composite elements. The mixing head performs anoscillating movement over the width of a lower outer layer and appliesthe still liquid reaction mixture to the lower outer layer by means of acasting rake or fan/spoon nozzle which is arranged at a right anglerelative to the mixing head and parallel to the lower outer layer.

The mixing head is fixed to a guide rail, the so-called portal, abovethe lower outer layer and is accelerated with the aid of electric motorsand slowed down before the reversal points. The raw materials forfoaming are fed to the mixing head via flexible hose lines. Furthermore,in some cases hydraulic or pneumatic hoses lead to the mixing head. Theraw materials for foaming are introduced into the mixing head vianozzles and are mixed.

The reaction mixture then flows into the casting rake and emergesthrough regularly spaced bores. As a result of the length of the castingrake and its bores, as well as the oscillating movement of the mixinghead, distribution of the reaction mixture obliquely to the productiondirection is achieved.

After application, the reaction mixture foams and rises to the upperouter layer. During the foaming process it bonds the two outer layersbefore the foam solidifies and cures.

This production process is limited in terms of manufacturing technologyas regards the production rate. Even if sufficiently strong motors,guide rails, hoses, mixing heads and casting rakes or fan/spoon nozzleswere used, the reaction mixture would be carried beyond the edges of theouter layers at the reversal points owing to excessively highcentrifugal forces. According to the prior art, production rates of morethan 15 m/minute cannot be achieved in the continuous production ofsandwich composite elements with this application technique.

The technique of increasing the production rate to up to 60 m/minute bymeans of stationary mixing head technology and rigid delivery systems issufficiently well known. This process is called US technology. UStechnology (high-speed machines) consists substantially of threeidentical metering lines with separate feed and separate mixing headsand delivery systems. However, this technology does not have adistributor head. This process further has the disadvantage that thereaction mixture emerging from each of the individual mixing heads canalso be subject to different physical conditions as regards pressure andtemperature, and this manifests itself in the resulting foam asreductions in product quality, such as, for example, uneven surface,smaller cells, different thermal conductivity values due to punctuallydifferent reaction kinetics.

EP 1 857 248 A2 solves that problem by not providing every dischargeline with a separate mixing head. Rather, only a central mixing head isprovided, via which a plurality of delivery lines are fed.

WO 2008/018787 A1 relates to a device for applying a viscous mixture toa surface by means of one or more outlet openings which are fed by afeed element.

The specification relates further to a process for the production of aninsulating element, comprising the steps of applying a viscous mixturewhich forms a foam on a substrate layer, the foam subsequently beingcrosslinked and the foam layer optionally being further coated. A mixinghead 3 is supplied with raw material with components from supply pipes 1and 2. Via a rigid main pipe 8, a casting rake 6 is controlled by aplurality of intermediate webs 5 via a sub-distributor 4. The castingrake is accordingly rigidly connected to the mixing head and can only bemoved to the left or right together with the mixing head in order toallow the application region to be adjusted as a whole to the correctposition relative to the substrate. Moreover, cleaning of the system isvery complex.

WO 2008/104492 A2 discloses a process for the production of compositeelements, wherein the application of the liquid starting material forthe isocyanate-based rigid foam is carried out by means of a stationarypipe which is arranged parallel and at a right angle to the direction ofmovement relative to the outer layer and is provided with bores.

In view of that prior art, the object of the present invention is todevelop devices and processes with which a high production rate can beachieved with a low layer thickness. A further object is to improve thesurface (especially as regards its homogeneity) as well as theabove-defined product qualities of the foams obtainable using suchdevices/processes.

That object is achieved in a first embodiment by a device for applyingfoaming reaction mixtures, comprising

(a) a mixing head for mixing raw materials for the production of thefoam,

(b) a distributor head located behind the mixing head in terms of flow,

(c) at least two, preferably at least three, particularly preferablyfrom three to eight, most preferably three or four, flexible hose linesattached to the distributor head, and

(d) at least two, preferably from two to eight, particularly preferablythree or four, stationary casting rakes for applying the mixture of rawmaterials for forming the foam to a moving substrate.

When the distributor head is described in this connection as beinglocated behind the mixing head, this is to be understood in relation tothe direction of flow of the material flowing through the two heads;that is to say, the material flows first through the mixing head andonly then through the distributor head.

For processing of the raw material there is used in particular an inertgas selected from the group air, nitrogen, carbon dioxide and noblegases such as argon and helium. Air is preferably used as chemicallyinert gas.

Depending on the technology used (high-pressure or low-pressure), themixing head can be in the form of a dynamic mixer or in the form of astatic mixer and serves in particular to intimately mix the component inquestion, or the mixture, with the inert gas that is under elevatedpressure. After introduction of the inert gas, the components on theirway to the distributor head, or the mixture of components on its way tothe mixing head, has/have an elevated pressure, which causes anincreased discharge rate of the foaming reaction mixture. In addition,the above-mentioned product qualities are improved.

The casting rakes used according to the invention each have a tube-likeshape and are each provided with holes distributed over the entirelength of the rake, and the holes are preferably oriented so that theyare at an angle of from 75° to 105°, particularly preferably at a rightangle (90°), relative to the lower outer layer. The reaction mixture isfed to the casting rake either at one end of the rake or in the middleor in a region in between.

In a preferred embodiment of the present invention, the casting rakesare arranged in a stationary manner transversely, in particular at anangle of 90°, to the production direction of the substrate. Thestationary arrangement of the casting rake has the advantage that thedensity is not changed at the edges of the applied foam as compared withother areas of the applied foam. Accordingly, the foam application iscontinuously extremely even over the entire width of the substrate.

The casting rakes can also be arranged transversely in an offset mannerin the production direction of the substrate, or they can be locatednext to one another in a line. In the case of an offset arrangement,overlapping of the casting rakes can lead to a lengthwise applicationgradient with a stepped pattern.

The casting rakes that are preferably used within the scope of thepresent invention have on the inside a conical flow cross-section whichtapers from the reaction mixture inlet to the furthermost bore, so thatthe flow pressure upstream of the outlet openings can be equalised.

Analogously to the prior art, the casting rakes used according to theinvention each preferably have a conical inner cross-section in theregion of the outlet opening of the foaming reaction mixture.Accordingly, the casting rakes correspond substantially to one-waycasting rakes known per se which have hitherto been used in the priorart for the oscillating application method.

In a second embodiment, the object underlying the invention is achievedby a process for the production of foaming reaction mixtures using adevice according to the invention.

There is preferably used as component A an isocyanate component. Thereis preferably used as component B a polyol component. In thisconnection, the expressions “isocyanate component” and “polyolcomponent” also include mixtures of different isocyanates and polyols,respectively. Polyurethane foams are thus obtained. In the presence ofspecific activators, isocyanates can also react with one another andform macromolecules having isocyanurate structures(polyisocyanurates=PIR). Because the reactions of isocyanates withpolyols and isocyanates can take place simultaneously or in immediatesuccession, macromolecules having urethane and isocyanurate structures(PIR-PUR) are obtained.

In the process according to the invention, the casting rakes arepreferably so arranged that the emerging foaming reaction mixture isapplied to a lower outer layer in the production direction of thesubstrate (direction of movement of the substrate).

Alternatively, the casting rakes are so fixed in the process accordingto the invention that the emerging foaming reaction mixture is appliedto a lower outer layer against the production direction of thesubstrate.

In both cases that is achieved by appropriately inclining the castingrake bores at an angle of from 45 to 135° relative to the substrate.

In a further preferred embodiment of the present invention, the devicecomprises at least two, preferably at least three, particularlypreferably from three to eight, most preferably three or four, flexiblehose lines of equal cross-section, of equal length and made of the samematerial which are attached to the distributor head. It is therebyensured that the same amount of raw material per unit time is introducedinto the casting rakes (at least two, preferably at least three,particularly preferably from three to eight, most preferably three orfour) and accordingly also applied to the substrate.

In a further embodiment, the object underlying the invention is achievedby a device for the production of sandwich composite elements comprisingat least two feed devices for in each case an upper and a lower outerlayer, a revolving upper belt for guiding the upper outer layer and arevolving lower belt for guiding the lower outer layer, on which thereare arranged one behind the other a device according to the invention, amoulding section and a cutting device.

The invention further provides a process for the production of foamedsandwich composite elements, wherein a device according to the inventionfor the production of sandwich composite elements is used.

In the device according to the invention, a mixing head is preferablyattached to a rigid frame above the lower outer layer, so that differentreaction profiles for the production of products of differentthicknesses are possible. To the mixing head, in which the individualcomponents for foaming are mixed together, there is fixed a distributorhead. The distributor head has, for example, at least two, preferably atleast three, particularly preferably from three to eight, mostpreferably three or four, flexible hose lines whose length,cross-section and material are preferably all identical. This has theadvantage that the foaming behaviour of the still liquid reactionmixture when it later comes into contact with the lower outer layer hasprogressed equally as far at each point of contact, which results inparticularly uniform foaming of the product that is produced. Thisadvantage is assisted not only by the identical length, cross-sectionand material of the flexible hose lines but also by the fact that allthe mixture that is to be applied emerges from the same mixing head.There can be used as the flexible hose line any material known to theperson skilled in the art that does not react with the reaction mixtureto be foamed and to which the reaction mixture does not adhere toogreatly. The material of the flexible hose line is preferably selectedfrom the group polyethylene (PE), polypropylene (PP), polyvinyl chloride(PVC), polyethylene terephthalate (PET), rubber, polytetrafluoroethylene(PTFE) and polyurethane (PU). Rubber is to be understood as being anyflexible rubber known to the person skilled in the art that can beprocessed to feed lines; nitrile-butadiene rubber (NBR) is preferred.Particular preference is given to a flexible material selected from thegroup PE, PP, PET and PVC. The flexible hose lines can be arranged onand fixed to a rigid frame arranged in the transverse direction to theproduction direction of the transport belt above the upper outer layer,so that they supply the casting rakes optimally with the reactionmixture and uniform application over the width of the lower outer layeris ensured. The flexible hose lines and the casting rakes areadvantageously arranged at a height of from 20 to 500 mm above the lowerouter layer and preferably in such a manner that the reaction mixture isapplied to the lower outer layer in such a manner that no unwetted areasoccur on the lower outer layer between the individual application areasof each of the casting rakes.

The discharge rate from the casting rakes is in particular from 1 to 5m/second. In a particular embodiment, both the mixing head and thedistributor head, including the flexible hose lines, can be so arrangedand fixed that it is also possible to produce products having athickness that decreases in the transverse direction to the productiondirection of the transport belt or having constantly changing thicknessratios. This can substantially be achieved by an appropriateconfiguration of the casting rakes. During foaming, those gaps betweenthe bores close, so that desired uneven foaming in the height of theproducts is possible.

As a result of this type of arrangement, a portal as is essential in thecase of an oscillating casting rake or fan/spoon nozzle can be omitted.Furthermore, with this arrangement, the production rates are dependentonly on the speed of the transport belt or the discharge rate of thefoaming machine and on the cross-section of the bores of the castingrakes. A further advantage of this device according to the invention ascompared with processes in which a plurality of mixing heads must beused is that, by the use of only one mixing head, no variations canoccur as a result of different processing pressures, temperatures or thelike, as a result of which the production safety and product quality arereduced.

Any mixing head known in the prior art can be used as the mixing headfor the device according to the invention. However, they must besuitable for the foaming in particular of the polyol component and theisocyanate component for the production of polyurethane sandwichcomposite elements. The chemically inert gas can be mixed with thereaction mixture in the mixing head or with one or both of the reactioncomponents beforehand in order to prevent possible clogging of theflexible hose lines. The chemically inert gas is selected from the groupnitrogen, air, carbon dioxide and noble gases such as argon and helium.Instead of a gas, other constituents can be mixed with the reactioncomponents. Such substances are selected, for example, from the groupgraphite, polyurethane flour, melamine, quartz sand, Al₂O₃, talcum, andnanocomposites such as, for example, layered silicates, nanotubes, andnanosand, and are added to the reaction components in particular in themixing head.

The material of the distributor head can be selected from the samematerial as the casting rakes, in particular from steel, stainlesssteel, aluminium and plastics materials. In each case, the chosenmaterial must withstand the usual pressures and temperatures in therange of from 20 to 40° C. that prevail in the mixing head. The geometryof the distributor head is preferably so chosen that the length of thepath from the distributor inlet to the respective outlets of theflexible hose lines to the bores of the casting rakes is equal.Furthermore, it is advantageous for the cross-sections of thedistributor head outlets to be identical for all the distributor headoutlets. The cross-section of the distributor head inlet, on the otherhand, can also be larger than the respective distributor head outlets.

The application device according to the invention can be a constituentof a further device which is used for the production of sandwichcomposite elements. The production of polyurethane sandwich elements(panels) is generally carried out in a continuous process. In thatprocess, the panels are produced continuously on so-called twintransport belts in thicknesses of generally approximately from 20 to 240mm. Thicknesses below 20 mm and above 240 mm are, however, alsopossible. Such a twin transport belt usually consists of a revolvingupper belt for guiding the upper outer layer, a revolving lower belt forguiding the lower outer layer, a feed device for the upper outer layer,a feed device for the lower outer layer, a moulding section in which thepolyurethane reaction mixture foams and reacts between the upper outerlayer and the lower outer layer, a cutting device for the panel that hasbeen produced, as well as a metering station having a mixing head forapplying the polyurethane reaction mixture to the lower outer layer.

The arrangement of the individual elements for a continuous process forthe production of sandwich composite elements is known from the priorart, as described in DE 1 247 612 A1 and DE 1 609 668 A1.

Within the context of the present invention, a sandwich compositeelement is understood as being a composite element which is composed atleast of two outer layers and an intermediate core layer.

Any materials known to the person skilled in the art can be used as thecore layer. Preference is given to fibreboards made of mineral fibres orsheets of rigid foam, such as, for example, rigid polyurethane orpolyisocyanurate (PIR) foam, polystyrene foam, phenolic resin foam.

In particular, sandwich composite elements consist at least of two outerlayers of rigid or flexible material and a core layer of a foam, suchas, for example, a rigid PUR foam. Rigid PUR foams are here to beunderstood as being rigid foams based on polyurethane compounds,polyurea compounds as well as polyisocyanurate compounds.

There are preferably chosen as the core layer rigid foams based onpolyurethane and/or polyisocyanurate. For the production of rigid foamscontaining polyurethane groups and/or polyisocyanurate groups there canbe used as starting components any compounds known to the person skilledin the art having NCO-containing compounds that are reactive towards OHcompounds, such as a) aliphatic, cycloaliphatic, araliphatic, aromaticand heterocyclic polyisocyanates, preferably diphenylmethanediisocyanate (MDI) or polyphenylpolymethylene polyisocyanates,polyisocyanates containing carbodiimide groups, urethane groups,allophanate groups, isocyanurate groups, urea groups or biuret groups,particularly preferably based on polyphenylpolymethylene polyisocyanate,and b) compounds containing at least two hydrogen atoms reactive towardsisocyanates and having a molecular weight in the range from 400 to10,000 g/mol, such as, for example, compounds containing amino groups,thiol groups, hydroxyl groups or carboxyl groups.

Moreover, it is possible to use suitable NCO prepolymers, prepared fromthe reaction of polymeric MDI with aliphatic or aromatic polyetherpolyols or polyester polyols, for example polyether polyols or polyesterpolyols containing from 1 to 4 hydroxyl groups and having anumber-average molecular weight of from 60 to 4000.

The production of the foams takes place using conventional auxiliarysubstances and additives known to the person skilled in the art, such ascatalysts, foaming agents, crosslinkers, flameproofing agents, foamstabilisers, flow improvers, inhibitors, as well as optionally solidadditives for improving the thermal conductivity and the flameprotection.

As materials for the outer layers there can be used any materials knownto the person skilled in the art. Preference is given to metals, such assteel (galvanised and/or lacquered), aluminium (lacquered and/oranodised), copper, stainless steel, or non-metals such as reinforced,non-reinforced and/or filled plastics materials, such as, for example,polyvinyl chloride or polyester- or glass-fibre-based, impregnatedcardboard, paper, wood, bitumen-impregnated glass nonwoven and mineralglass nonwoven.

For example, the outer layers can be coated with a lacquer.

Also suitable as outer layers are combinations of the outer layers onthe respective sides of the panel produced from the above-mentionedmaterials.

Such composite elements based on different outer layers (rigid orflexible) and a core layer of rigid polyurethane foam are sufficientlywell known from the prior art and are also referred to as metalcomposite elements or insulating boards. Further layers can be providedbetween the core layer and the outer layers.

Examples of the application of such composite elements having rigidouter layers are flat or lined wall elements as well as profiled roofelements for the construction of factory buildings and refrigeratedwarehouses. The composite elements are also used as trucksuperstructures, warehouse doors and gates as well as in containerconstruction. Insulating boards as well as composite elements havingflexible outer layers are used as insulating materials for roofs,outside walls and as flooring panels.

The production of such composite elements by a continuous ordiscontinuous process is sufficiently well known from the prior art. Tothat end, the still liquid reaction mixture is applied to the lowerouter layer (substrate) by means of the device according to theinvention. The reaction mixture, which is now slowly foaming, istransported on the lower outer layer by means of a lower belt into themoulding section, which is spanned by an upper belt and a lower belt.The foaming reaction mixture reaches the upper outer layer andaccordingly bonds the two outer layers to one another. Within themoulding section, wherein the upper belt and the lower belt define thethickness of the product that is to be produced, the foam solidifiesand, after passing through the moulding section, is cut to length by acutting device for cutting the panels so produced to desired lengths.

EXAMPLES

The homogeneity of the surface is classified by determining the faultdensity. To that end, the size and number of blisters on the upper sideof the foam is determined in an area measuring 200 mm×1000 mm and thefault density is thereby defined as follows:

The blisters are subdivided into four size categories:

Blister category 1 Blisters having a surface area of up to about 1 cm²

Blister category 2 Blisters having a surface area of approximately from1 to 3 cm²

Blister category 3 Blisters having a surface area of approximately from3 to 5 cm²

Blister category 4 Blisters having a surface area of approximately ≧5cm²

Comparison Example 1

Fault density of the upper sides of the foam in metal composite elementsproduced using an oscillating casting rake.

Comparison Example 2

Fault density of the upper sides of the foam in metal composite elementsproduced using a device comprising a mixing head, a distributor headlocated behind the mixing head in terms of flow, eight discharge linesattached to the distributor head, which are fastened transversely to theoutflow direction on a frame that is rigid (i.e. a device without acasting rake).

Example 3 According to the Invention

Fault density of the upper sides of the foam in metal composite elementsproduced using a device comprising a mixing head (10), a distributorhead (20) located behind the mixing head in terms of flow, threeflexible hose lines (30 a, 30 b, 30 c) attached to the distributor head,and three stationary casting rakes (40 a, 40 b, 40 c) for applying themixture of raw materials for forming the foam to a moving substrate.FIG. 1 is a schematic illustration of the foregoing components of thedevice used in this Example.

The following result shown in Table 1 was determined by means of in eachcase twenty series of tests relating to the respective processes forproducing metal composite elements using a commercially available rigidpolyurethane foam system.

TABLE 1 Fault density of the upper sides of the foam in metal compositeelements 1 2 (comparison) (comparison) 3 Oscillating 8 lines, 3 linesand casting without a 3 stationary Example rake casting rake castingrakes Blister category Amount [%] Amount [%] Amount [%] 1 2-3 2-3 1-2 25-7 4-5 1-2 3 10-15 2-3 <1 4 2-3 1 <1

What is claimed is:
 1. A device for applying a foaming reaction mixture,comprising (a) a mixing head for mixing raw materials to produce thefoaming mixture, (b) a distributor head located behind the mixing headin a manner such that the foaming mixture will flow from the mixing headto the distributor head, (c) at least two flexible hose lines attachedto the distributor head, and (d) at least two stationary casting rakesconnected to the flexible hose lines for receiving foaming mixture fromthe hose lines and for applying the foaming mixture to a movingsubstrate.
 2. The device of claim 1 in which there are at least threeflexible hose lines attached to the distributor head, and at least threestationary casting rakes for applying the foaming mixture to the movingsubstrate.
 3. The device of claim 1, in which the casting rakes arearranged transversely to the production direction of the substrate. 4.The device of claim 1, in which the arrangement of the casting rakes isoffset in the direction of the substrate.
 5. The device of claim 1, inwhich the casting rakes are located next to one another in a linetransverse to the direction of the substrate.
 6. The device of claim 1,in which the casting rakes have a conical inner cross-section near anoutlet opening for the foaming mixture.
 7. The device of claim 1, inwhich the casting rakes have an internal conical cross-section from thefoaming mixture inlet to the casting rakes' furthermost bore.
 8. Thedevice of claim 1, in which there are at least three flexible hose linesof equal cross-section and of equal length that are made of the samematerial which are attached to the distributor head.
 9. Apparatus forthe production of sandwich composite elements, comprising: (a) at leasttwo feed devices for an upper and a lower outer layer, (b) a revolvingupper belt for guiding the upper outer layer and (c) a revolving lowerbelt for guiding the lower outer layer, on which there is arranged (d)the device of claim 1 positioned to apply foaming mixture to the lowerouter layer, (e) a moulding section and (f) a cutting device.
 10. Thedevice of claim 2 in which the casting rakes are arranged transverselyto the direction of the substrate.
 11. The device of claim 10 in whichthe arrangement of the casting rakes is offset in the direction of thesubstrate.
 12. The device of claim 10 in which the casting rakes arelocated next to one another in a line transversely to the direction ofthe substrate.
 13. The device of claim 10 in which the casting rakeshave a conical inner cross-section near an outlet opening for thefoaming mixture.
 14. The device of claim 10 in which the casting rakeshave an internal conical cross-section from the foaming mixture inlet tothe casting rakes' furthermost bore.
 15. The device of claim 10 in whichthere are at least three flexible hose lines of equal cross-section andof equal length that are made of the same material which are attached tothe distributor head.